Disorders of organs or tissue of the gastrointestinal tract can be caused by as neurological factors (such as abnormal nerve impulses) or by physical factors (such as excess tissue volume).
For example, intestinal motility (i.e., the contraction of intestinal muscles and the propulsion and movement of the lumenal contents) is controlled by nerves and hormones, as well as by electrical activity in the muscular wall of the intestine. There are several disorders that involve abnormal motility and result in abnormal and uncomfortable visceral sensations. These disorders can cause significant discomfort and distress in the absence of gross physical abnormality of the intestine.
For example, irritable bowel syndrome (IBS) is a common disorder of the intestines. IBS can lead to crampy pain, gassiness, bloating, and changes in bowel habits. Some people with IBS have constipation (difficult or infrequent bowel movements) others have diarrhea (frequent loose stools, often with an urgent need to move the bowels); and some people experience both symptoms intermittently. Sometimes the person with IBS has a crampy urge to move the bowels, but cannot do so. The cause of IBS is not known, and as yet there is no cure. IBS can be characterized as a functional disorder because there is no sign of disease when the intestine is examined, often IBS is just a mild annoyance, but for some people it can be disabling.
Dyspepsia is another example. Dyspepsia is literally translated as ‘bad digestion” and is commonly known as indigestion. Motility-like dyspepsia causes persistent or recurring abdominal pain that is centered in the upper abdomen. People with motility associated dyspepsia also may experience bloating, nausea, burping and a feeling of fullness that occurs soon after eating. It is an extremely common symptom complex, affecting as much as one-fourth of the United States adult population.
There are other disorders affecting the gastrointestinal tract that are characterized by abnormal tissue conditions not associated with neural abnormalities.